For example, a Time Of Flight Mass Spectrometer (TOF-MS) as an example of a measurement apparatus using an A/D converter is an apparatus which analyzes a component included in a sample by ionization and accelerating the sample at a constant voltage, and measuring the flight time and the signal intensity according to mass and electrical charge of the sample. In the TOF-MS, since waveforms of detection signals differ according to the number of ions detected at a time, data acquisition of ADC (analog to digital converter) system is generally used in order to measure the detection signal quantitatively. The data acquisition system of ADC system is a system which acquires digital data showing time data and a voltage value of an ion detection signal by sampling the ion detection signal which is an analog signal at a constant cycle using the A/D converter.
In resent mass spectrometers, according to sensitivity improvement of the ion detector, the intensity difference of an ion signal to be measured increases. Accordingly, an A/D converter which can perform sampling to a wide voltage range with high precision at high speed is required. However, there is a problem that, since the effective number of bits of a high-speed (1 to 2 Gsps) A/D converter commercially available is only about 8 to 10 bits, a dynamic range (signal intensity resolution) becomes deficient in such measurement that intensity of a detection signal changes at least dozens of times, so that measurement sensitivity (S/N ratio) degrades largely.
Generally, in order to realize an extremely-high dynamic range, such a problem is solved by using a plurality of A/D converters, but when a plurality of A/D converters are used, the number of steps for designing, members cost and the like of a fast hardware are increased, so that high cost and lengthening of a development period become problematic.